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Old 06-22-2020, 08:30 AM   #1
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Anti-Freeze and water heater

I commissioned my boat (FINALLY) this weekend. While flushing the anti-freeze from the water lines, I started to get a lot of brown water from the hot side when I switched the off the water heater bypass. The sediment clogged the strainers in my sinks.

I removed the water heater, flushed out the sediment and replaced the heating element (I also turned the water heater on accidentally while it was empty).

My water heater is electric and runs off of the closed cooling side of the engine.

In order to remove the water heater I lost a decent amount of engine antifreeze. Do I need to do anything special to refill that system? Will it require bleeding?

My assumption is that I fill the heater exchanger, start the engine and let it run for a few minutes, then shut down the engine, top off the heat exchanger and fill the overflow resevior to the Full (Cold) fill line.

Any feedback would be greatly appreciated.
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Old 06-22-2020, 08:47 AM   #2
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Normally for any engine that self bleeds well, I fill it, start it with the cap off. Top it off again while running as the level will drop after start. As soon as the level is steady, cap it, let it warm up fully, then shut down and let it cool. Make sure coolant level in the heat exchanger and overflow tank are both good after cooldown.
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Old 06-22-2020, 09:18 AM   #3
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In the future, drain and bypass the water heater instead of running anit-freeze through it...'cuz if you don't flush ALL the antifreeze out of it, it the hot water can taste and smell of antifreeze and it can even damage the thermostat and heating element.


Bypass kits are available online and from some marine retailers.


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Old 06-22-2020, 09:58 AM   #4
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In the future, drain and bypass the water heater instead of running anit-freeze through it...'cuz if you don't flush ALL the antifreeze out of it, it the hot water can taste and smell of antifreeze and it can even damage the thermostat and heating element.


Bypass kits are available online and from some marine retailers.


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Thanks Peggy!! Always love to hear from you. I have a bypass kit and do bypass it when I run propylene glycol in the freshwater system. I drain the water heater by opening the pressure valve and the drain spigot.

What I spilled was the engine AF that heats the water in the water heater when the engine is running.
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Old 06-22-2020, 10:12 AM   #5
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Years ago I plumbed my engine's coolant to the water heater as the factory hadn't done so. I ran it at about a 1,000 rpm at the dock and vented as best I could but still no flow through the water heater's coil- the hose was cold.

I asked on boatdiesel what to do and they said take it out and run it hard for ten minutes. I did and it started heating. After it cooled down a bit I opened the fill cap and added more antifreeze as well as in the overflow bottle. Worked fine from that point forward.

So try that if venting and low rpms doesn't get the flow started. But if the hose is hot, then you have flow, so just top it off with antifreeze.

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Old 06-22-2020, 10:26 AM   #6
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I have a "T" in the hose going to the hot water tank with a valve and coupling.

I hook up a pump to the "T" and stick the inlet hose into a bucket of coolant and pump the antifreeze into the system. Since it's filling from the lowest point, all air gets pushed up and out of the expansion tank.

To drain, I reverse pump orientation. Also use the "T" for reverse flushing the engine.
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Old 06-22-2020, 11:32 AM   #7
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Shrew,
According to Tony Athens from Seaboard Marine, to properly remove air from your cooling system may require a run around the harbour "under load" as compared to running at dock. Leave the cap off or at least loose, fill the expansion tank to within an inch of the top and monitor it carefully while running slowly around the harbour. Top off as needed. Once stabilized (level no longer dropping) fill and put cap on tight. Add some antifreeze to the overflow bottle. After it has all cooled, check both levels again and add/adjust as needed.

I would try this method, prior to trying the "run it hard" method that David described. Also, keep an eye on engine temps, as having a really stubborn air lock could lead to an overheat, and you don't want that.
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Old 06-22-2020, 11:41 AM   #8
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I think it was Tony who recommended how to vent my system. I did forget to mention leaving the cap loose and I really meant to run it a high cruising speed for ten minutes to get it up to temperature and vent it. It needs to run at a high enough rpm to create enough pump pressure to blow out the air back to the main heat exchanger. Don't run it for long and watch the temp gauge.

Firehoser, thanks for clarifying the proper procedure.

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Old 06-22-2020, 11:59 AM   #9
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Another way to remove air from an engine is with a coolant pressure tester. Stick it into the expansion tank opening and pressurize the system and run the engine. The positive pressure compresses the air and moves it up into the expansion tank faster.
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Old 06-22-2020, 12:59 PM   #10
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Some engines have a coolant drain fitting on the low side of the block. A device that many "pros" have is a hand coolant pump with fitting inserted in that hole. Then with cap off you're filling from bottom. As best I remember the pump reservoir holds about a gallon. Most air lock problem areas when filling from top become a non issue when filling from bottom. Kinda like filling a stern drive.
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Old 06-22-2020, 02:34 PM   #11
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What I spilled was the engine AF that heats the water in the water heater when the engine is running.

Ooops...I missed that when I read your post. Oh well...maybe someone else can make good use of my winterizing advice.



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Old 06-22-2020, 02:42 PM   #12
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OK, I think I got it.

1) Crack filler cap on the coolant tank.

2) fill antifreeze in overflow bottle

3) Take the boat out for a short run at moderate RPM's.

4) watch overflow tank in order to either refill or to determine when it stops dropping.

5) Once overflow tank stops dropping, shut down and let engine cool

6) top off coolant tank

7) fill or drain overflow tank until it is at Full Cold.

Does that sound about right?
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Old 06-22-2020, 02:49 PM   #13
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I wouldn't take the boat out during the process, just run the RPMs up a bit at the dock if it doesn't self-bleed at idle. Not knowing exactly how your system is plumbed and how well your engine naturally bleeds, it's hard to say how much effort it'll take to get the air out.

The overflow tank also typically won't drop until after shutdown when things are cooling. That's why it's important to start the engine with the heat exchanger cap off and top off there as needed until the level stays steady, then you can cap it and let the system build pressure. Monitor the overflow tank over the next couple of heat cycles, as small amounts of remaining air may bleed out.
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Old 06-22-2020, 07:59 PM   #14
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Shrew,
See post #7 and #8. No need to put any in the overflow bottle to start with. Fill expansion tank to within about 1 inch of full (top). Operate the engine under load, by motoring around the harbour with the cap loose or off. Monitor the engine temp, and add antifreeze if (when) the level drops. When it stabilizes, fill the expansion tank and put the cap on fully. Don't burn your self. After cooled, add coolant as needed and fill the overflow tank to the cold mark. Keep an eye on the coolant level for the next couple of trips. Don't overheat the engine during the "purging", so monitor temperatures carefully.
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Old 06-23-2020, 04:28 PM   #15
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Incidentally.....why 'under load'? Will there not be enough pressure to work out the air pocket at idle? Is revving the engine at the dock an issue??
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Old 06-23-2020, 04:54 PM   #16
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I think that the thermostat on some engines being closed because of a cold engine hinders bleeding air until the engine warms and thermostat opens. I take the thermostat out while reverse flushing the engine to eliminate the thermostat blocking flow.

As I stated earlier, I fill from the lowest point so trapped air is not an issue.

Next time the thermostat is out check to see if there is a small hole on it. If no hole, I drill an 1/8" hole in the thermostat to allow air to pass. The hole will not affect the thermostats operation but makes it easier to bleed air.

On the Lehman 120, there is a petcock on the highest point of the manifold to bleed air.
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Old 06-23-2020, 04:55 PM   #17
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Yes, some engines won't bleed properly until the t-stat is open. Some have a small air bypass or a bleed valve. A 1/16" hole in the t-stat does the trick too (I've found 1/8 slows warmup noticeably on some engines).
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Old 06-23-2020, 07:01 PM   #18
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Others have hit it. On some engines you cannot bleed the air without the thermostat opening and it is very difficult to get the engine up to full operating temps without a load. You need to have the coolant circulating completely to purge the air (on some engines).
My engine has an air bleed up high near the expansion tank that is opened up while filling slowly. This helps alot with allowing the air to escape. Then I follow the above to allow any trapped air to escape. Don't want an airlock causing an overheat!
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Old 06-23-2020, 07:24 PM   #19
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When I replaced my water heater I used gravity feed to fill in the water heater heat exchanger and hoses before reconnecing hoses to the engine, easy to do, peace of mind.

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Old 06-29-2020, 08:10 AM   #20
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So this turned out to be interesting. I thought I had drained maybe a quart, so I started my engine, however the alarm tone never shut off. I immediately shut it down and checked coolant. I couldn't see it but couldn't feel it for as far as I could stick my finger in there.

I started to fill the tank, it ended up taking almost 1.5 gallons before it was full. I re-evaluated my engine and realize my water heater is lower than the engine. I drained the engine engine through the water heater when I pulled the hoses. The pressure water hoses were blocking my view at the time and it drained significantly faster than I expected.

Once full I started the engine. The alarm tone stopped. I idled at the dock and as fluid dropped, I kept topping it off. I kept doing this until it stopped bubbling and stopped dropping. coolant hoses to the hot water heater were hot as well.

I filled the overflow tank and took the boat out. Temps ran fine, even after getting her up to 2900 RPM for 5 min. Water in water tank was hot. I shut it down and let it get cold. I checked the following morning. expansion tank was full, overflow tank had fluid in it.

I suspect I have a bypass on my thermostat. I seem to have solved the issue, unless I'm overlooking something.
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